Force Choke is an early level of the infamous Force Grip ability. Like Grip, it is used to telekinetically 'grip' one or more of the target's internal organs and apply pressure. However the target is not lifted or moved about. The area affected is typically the target's neck. It causes immobilization and choking, which with prolonged focus, can lead to death.
The reason why Darksiders usually use it instead of Grip is when they feel the need to just punish, threat, or scare their target, without wanting to cause death. It tends to be an effective demonstration of their power to unbelievers.